The invention relates to a method for controlling an automatic transmission driven by an internal combustion engine in which a shift from a first to a second transmission ratio occurs in the form of a pull upshift. Here a first clutch opens and a second one closes and an electronic transmission control device controls, via electromagnetic valves, the pressure curve of the first and of the second clutch during the shifting operation. The latter consists of a rapid-filling, a filling-equalization, a load transfer, a gradient-setting, a sliding, a gradient-reduction and a closing phase.
Such a method is known already from the Applicant""s laid open application DE 44 24 456 A1 which is included by explicit reference in the contents of the preamble of the instant patent application. In this publication is particularly proposed to use this method in a group transmission.
From the prior art (xe2x80x9cThe Engine Interventionxe2x80x9dxe2x80x94a new element of the electronic transmission control by Manfred Schwab and Alfred Mxc3xcller, Bosch, Technical Reports 7, 1983, pp. 166 to 174) is known, in general, to effect an engine intervention during a shifting operation, it being possible by an exactly time controlled curve of the engine torque during shifting operation of an automatic transmission to optimize the control of the transmission with regard to shifting comfort, service life of the friction elements and to the transmissible power of the transmission. By engine intervention is to be understood all steps which, during a shifting operation in the transmission, allow purposefully to modulate, especially to reduce, the engine torque generated by the combustion process. Due to the legislator""s strict requirement on the reaction time and the time cycle of the control during a total duration of the intervention of only about 500 ms, a precisely timed coordination of the shifting operation is required. An engine intervention can be used both in upshifts and downshifts. The primary object of the engine intervention in upshifts is to reduce the energy loss produced in the friction elements during the shifting operation by reducing the engine torque during the synchronization process without interrupting the traction. The tolerance obtained thereby can be used to increase the service life of the friction partners by abbreviating the grinding time.
From DE 42 09 091 A1 is further known already a method for reducing the engine torque during a gear shift in a motor vehicle. The energy torque which results from rotating masses to be retarded or accelerated during a change of speed of the rotation angle of the engine determined by a gear change is calculated and the engine torque is reduced during coupling of the new transmission gear by the amount of the energy torque.
Methods of the above mentioned kind are subject to constant further developments with regard to an optimal use of the engine intervention with the smallest possible load of the shifting elements, the same as an optimal torque curve that takes into account the directives of the engine manufacturer, especially in relation to the limits of the maximum possible engine intervention with regard to mixture and exhaust conditions.
The problem to be solved by this invention is to indicate an optimized use of the engine intervention especially requiring a minimal adaptation expense, that is, in an analytic calculation process, for ex., the fewest possible parameters are needed.
According to the invention, this problem is solved in a method of the kind above indicated with an engine intervention by a reduction of the engine torque occurring within the gradient-setting, sliding, gradient-reduction and closing phases, an engine intervention factor being transmitted from the transmission control device to an engine control device of the internal combustion engine. Thereby is advantageously obtained that the pressure curve set of the second, closing clutch and the friction torque resulting therefrom, the same as the torque generated by the intervention factor and emitted by the engine, is optimally matched in time without need of expensive adaptation parameters and expense.
In one development of the invention, it is proposed that a maximum engine intervention factor mdzegsomax be calculated from a maximum dynamic torque M_DYN, a static torque without engine intervention M_STAT and a maximum adjustable engine characteristic factor KF_MDZ MAX.
The maximum engine intervention factor mdzegsomax is calculated as the ratio of the dynamic engine torque M_DYN to the static engine torque M_STAT.
This applies to the case that the value thus calculated be smaller than the maximum adjustable engine characteristic factor KF_MDZ MAX. But in case the value, thus calculated, is greater than the maximum adjustable engine characteristic factor KF_MDZ MAX, then the maximum engine intervention factor mdzegsomax corresponds to the maximum adjustable engine characteristic factor KF_MDZ MAX.
In a special development of the invention is proposed that the engine intervention factor mdzegs in the gradient-setting phase GE be linearly increased all along beginning from a value zero to the value of the maximum engine intervention factor mdzegsomax. In the sliding phase GL that follows, the engine intervention factor mdzegs is maintained essentially constant at the value mdzegsomax and in the gradient-reduction phase GA and closing phase S that follow the engine intervention factor mdzegs is reduced from the maximum engine intervention factor mdzegsomax to the value zero.
The pressure on the second clutch P_K to close is advantageously calculated from the static engine torque with engine intervention M_STAT ME, the dynamic engine torque M_DYN, a factor F1 and a converter reinforcement WV, the same as the absolute pressure P_ABS.
The static engine torque with engine intervention M_STAT ME is calculated as the product from the static engine torque M_STAT by the sum of one minus the engine intervention factor mdzegs.
The clutch pressure P_K at the start of the engine intervention, namely, at the start of the GE phase, is calculated as the sum of the absolute pressure P_ABS and the static engine pressure P_M STAT which is calculated as product from the factor F1 by the static engine pressure M_STAT by the converter reinforcement WV, the absolute pressure P_ABS being the pressure required to overcome the recoil spring tensions and the friction on the actuating piston.
The clutch pressure P_K during the sliding phase GL is calculated as the sum of the absolute pressure P_ABS and the pressure P_M STAT ME of the static engine torque with engine intervention and the pressure P_M DYN of the dynamic engine torque, the pressure P_M DYN being calculated as the product from the factor F1 by the converter reinforcement WV by the dynamic engine torque M_DYN.
According to the invention the pressure of the second closing clutch during the pull upshift takes the following course: In the rapid-filling phase SF, the clutch is loaded with high pressure, in the filling-equalization phase FA; it is filled to a lower pressure level P_ABS and, in the load-transfer phase Lxc3x9c, the pressure is increased to an end value P_ABS+P_M STAT. In the gradient-setting phase GE, the pressure is increased from the value P_ABS+P_M STAT to a new end value P_ABS+P_M STAT ME +P_M DYN and in the sliding phase GL be kept constant until reaching a pre-synchronizer point VSYNC. Then follows the gradient-reduction phase GA in which the pressure is reduced to an end value P_ABS+P_M STAT and upon reaching the end value the closing phases S1 and S2 begin.
It is proposed in a development of the invention that the beginning of the engine intervention for synchronization with the shifting pressure build-up in the phases GE and GL be delayed, via a time step, when the reaction for the engine intervention is quicker than the reaction to the pressure directives. Thereby is advantageously obtained that the output torque be not unnecessarily reduced.
In reversal of the above mentioned features, it is proposed that the beginning of the shifting pressure build-up for synchronization with the engine intervention in the phases GE and GL be delayed, via a time step, when the reaction of the engine intervention is slower than the reaction to the pressure directives. Thereby unnecessary friction stresses on the shifting elements can be advantageously prevented.
In a development of the invention, the dynamic engine torque M_DYN is increased during the gradient-setting phase GE from 0 to 100%, in the sliding phase GL it remains at 100% and, in the gradient-reduction phase GA that follows, the dynamic engine torque M_DYN is again reduced from 100% to 0.
The engine intervention for the rest is activated only when the engine rotational speed exceeds a preset value whereby a stalling of the engine is advantageously prevented.
The maximum possible engine intervention factor mdzegsomax is advantageously stored in a characteristic field according to operating parameters such as of the engine rotational speed, of the load position, or of the injection amount, or of the engine torque, or of the air mass.
The maximum adjustable engine characteristic factor KF_MDZ MAX is reported back from the engine control device to the transmission control device whereby a quick regulation of the engine intervention factor is made possible.